Low-temperature annealing process for reducing stress of glass-metal connection sealing structure

Abstract

The invention discloses a low-temperature annealing process for reducing stress of a glass-metal connection sealing structure. The low-temperature annealing process comprises the following steps: 1, putting a connected and sealed glass-metal connection sealing section into an annealing furnace; 2, increasing the temperature to 200 DEG C from the room temperature; 3, increasing the temperature to 350 DEG C from 200 DEG C; 4, increasing the temperature to 450 DEG C from 350 DEG C; 5, increasing the temperature to 520 DEG C from 450 DEG C; 6, reducing the temperature to 470 DEG C from 520 DEG C;7, reducing the temperature to 370 DEG C from 470 DEG C; 8, reducing the temperature to 300 DEG C from 370 DEG C; and 9, reducing the temperature to the room temperature from 300 DEG C. According to the invention, the glass metal connection sealing part is subjected to annealing treatment at the temperature below the glass strain point, so that the stress value of the connection sealing part is greatly reduced, the safety and the reliability of the connection sealing part are improved, the qualification rate of the product is improved, and the effective life of the whole product is prolonged.

Description

technical field [0001] The invention relates to the technical field of annealing technology for a glass-metal sealing structure of a heat collecting tube, in particular to a low-temperature annealing process for reducing the stress of a glass-metal sealing structure. Background technique [0002] The medium-high temperature solar collector tube is mainly composed of a glass outer tube with an anti-reflection coating and a metal inner tube with a solar selective absorption coating. The reliability affects the normal operation of the power station to a large extent. The weakest part of the heat collector is the glass-metal seal used to connect the glass outer tube and the metal inner tube. Due to the essential difference in the physical properties of glass and metal, The two cannot achieve complete agreement in terms of linear expansion, so a certain structural stress will inevitably be generated during the sealing process. The existence of structural stress is a very big hidd...

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Problems solved by technology

[0002] The medium-high temperature solar collector tube is mainly composed of a glass outer tube with an anti-reflection coating and a metal inner tube with a solar selective absorption coating. The reliability affects the normal operation of the power station to a large extent. The weakest part of the heat collector is the glass-metal seal used to connect the glass outer tube and the metal inner tube. Due to the essential difference in the physical properties of glass and metal, The two cannot achieve complete agreement in terms of linear expansion, so a certain structural stress will inevitably be generated during the sealing process. The existence of structural stress is a very big hidden danger for the heat collector. Once the stress exceeds a certain Released under a special situation, cracks will occur at the sealing part, and it will be directly damaged if the sealing part is damaged. Once the sealing part is damaged, the vacuum built by the glass outer tube and the metal inner tube will disappear, thus making the solar energy selective. The absorbing coating is directly exposed to the air. This high-temperature oxidation environment will accelerate the aging and attenuation of the film layer. In addition, due to the absence of the protection of the vacuum environment, the metal inner tube will also lose a large amount of light energy to the outside while absorbing it. Heat energy, that is, heat loss increases, which greatly reduces the light-to-heat conversion efficiency of the heat collecting tube, affects the service life of the heat collecting tube, and increases the cost of use

[0003] Since the coefficient of linear expansion between glass and metal only matches within a certain temperature range, corresponding structural stress will inevitably be generated. If the structural stress is too large, the temporary stress generated by thermal shock and the If the structural stress is superimposed, it is very likely to cause the glass at the seal to break. Usually, the annealing temperature of borosilicate glass is 550±10°C. At this temperature, the glass tube and the seal are annealed. The stress can be eliminated, but the stress value of the glass-metal seal after annealing shows a large fluctuation of the stress value compared with that before annealing. It is not large, only about 10%, so that the stress of the sealing part is still in the dangerous range of 160-180nm / cm (Note: This unit represents the birefringent optical path difference, which is generally considered to be temporary caused by the external temperature difference when it is greater than 120nm / cm The resultant force of stress and structural stress may cause the glass to burst)

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